Coated fabric



Patented Dec. 7, 1943 COATED FABRIC Robert L. Lester, N ewburgh, N. Y.,assignor to E. I. du Pont de Nemours & Company, Wilmington, De1., acorporation of Delaware No Drawing. Application August 20, 1941, 'SerialNo. 407,608

3 Claims. (01.117-166) This invention relates to the production ofcoated fabrics, and more particularly to the production of shade clothfor window shades and the like, having improved properties.

Window shade cloth comprising a textile fabric coated with acellulosenitrate composition is well known in the art of coated fabrics and hasbeen developed to a point where it is considered generally satisfactory.However, there is need for improvement where the shade cloth issubjected to sunlight exposure over a long period of time. A seriousobjection of the present-day material is technically referred to astendering. By tendering is meant that a shade cloth loses afterprolonged exposure to sunlight much of its original tensile strength. Afurther objection of the prior art material is a lack of colorstability, particularly in the case of white and other light coloredtranslucent shade cloth materials.

It is well known that zinc oxide is an excellent filter for ultra violetlight and, for this reason, it has been used quite extensively inpyroxylin ments have been reduced to less than the wave length of ultraviolet light which is less than 4,000 angstroms which corresponds to .4micron. In a systematic study of the effect of the taining suchpigments, it was found thatparticles coatings for window shade materialto filter ultra violet light which is known to have a deleterious veffect on nitrocellulose. By the use of zinc oxide in pyroxylln coatingsfor window shade material definite improvements have been made withrespect to tendering. However, there is need for further improvementsince the grades of zinc oxide normally used do not give completelysatisfactory results withres'pect to tendering andcolor stability.

An object of the present invention is the provision of an improved shadecloth material. A

terialhaving great resistance to color change,

particularly in the case of white and other light coloredshade'cloth'material, when exposed to sunlight over a prolonged period.

having a greater diameter than .4 micron or in the case ofacicularshaped particles, those having a width greater than .4 micron,deteriorated less than similar material containingv zinc oxide particlesless than .4 micron under simultaneeous conditions of exposure. It wasalso discovered that there was greater color stability in the case ofthe material employing the larger particles of zinc oxide.

An accelerated test for window shade material is obtained by exposingthe material at Hialeah, Florida, in a closed box with a glass cover fora period of 40 weeks. The material is positioned in the box four inchesfrom the glass at an angle of 45 and facing south. The surfacetemperature of the window shade material when exposed posed to'in actualservice.

a The objects of this invention are accomplished by coatingjeach side ora textile fabric base material with a liquid coating compositioncomprising a solution of nitrocellulose, a plasticizer, and pigment. Atleast 20% of the total pigment in the coating composition consists ofzincoxide parti'cleathe size of which is greater than .4

, micron in any one'direction.

gloss of the coating. The particle size ot'pigunder these conditionsoften reaches 200 F. due to lack of circulation of air inside theexposure box. This temperature is far in excess of any temperature thewindowshade material is ex- The exposure in Florido. as describedcorresponds to approximately 10 years of service under normalconditions.

The following examples are given to illustrate specific embodiments ofthe invention, although it is to be understood that the invention is inno way limited to these particular examples.

To a suitable sheeting, such as one running 4.95 yards per pound at a'width of 37 /2 inches, and having a thread count of 68 x 72, is appliedby means of a doctor knife on each side a total of 0.3 to 0.8 ounce, dryweight, per square yard, which corresponds to a total of 0.6 to 1.6ounces per square yard on both sides of a suitable liquid coatingcomposition. After the volatile solvents of the coating composition areexpelled by pass .fl m bontain'jng the larger particles did the fabriccorresponds to 1.2 to 3.2 ounces per square yard.

cial use and material which deteriorates less than 35% upon 40 weeks ofFlorida exposure is considered satisfactory for commercial use and isacceptable to the trade in general.

In the case of the so-called opaque material the drycoating compositionmay be as follows:

Parts by'weight Cellulose nitrate 43.0-25.0 Pigment 45.0-56. Dibutylphthalate 12.0-18.7

The method of preparing the above compositions which comprisesdissolving. the cellulose nitrate in organic solvents to form a solutionandgrinding the pigment'in the plasticizer before blending withthe'solution is well known in the art and forms no part of the presentinvention and a detailed description of such method does not appear tobe necessary.

Duplicate samples of white translucent window shade material were madeemploying nodular shaped zinc oxide as the total pigment content. In onecase the diameter'of the zinc oxide pigment particles corresponded to1.0 to 1.5 microns and in' the other case the diameter of the 'zincoxide pigment particles corresponded to .25 to .30micron. Both materialswere exposed slmultaneously at Hialeah, Florida, under glass and fourinches from the glass facing. south at an angle of 45 fora period of 40weeks. The tensile strength of each material was measured beforeexposure, at the end of 20 weeks exposure, and at the end of 40 weeksexposure.

' The following table indicates the results of deterioration of tensilestrength of window shade 55 material employing nodular shaped zinc oxideIn the case oftranslucent window shade vma- The fqlldwingtablelmdicatfas n' terial the dry coating composition may be as foltaimfd wlflh aclcula'l' Shaped Zmc oxlde wf lows. particles incorporatedin the coating composltlon.

.' Inasmuch as acicular zinc oxide particles are not Parts y weightavailable in widths less than .4 micron, the

Cellulose n t 110 nodular shaped zinc oxide having a diameter Pigmen V dof .25 to .30 micron -was'employed as a control yl p h l t 2B.231. 4 fth following t Initial tensile V Tensile strength after weeks ,Tensilestrength after 40 weeks strength 4 ,Florida exposure Florida exposureParticular size-oi ziil c oxide particles in mg Per cent Per cent W- nF- W. F. W. and F. deterlora- W. F. W. and F. deterioration tion Nodular(diameter):

.25 to .30 micron 68 46 114 57 35 92 19 4a 19 67 41 Acicular Width .54micron, length 3.2 mlcrons 73 46 119 -7 4 3 1 3 37 00 a 1 Width .43micron, length 3.2 microns.-- 69 46 115 7 103 v 6 2 3 g 5 Width .43micron. length 3.2 microns--. 67 42 l 109 2 40 102 6 l 3 3 99 9 At theend of the 40 weeks exposure in Florida,

the'original tensile strength-of the window shade material containingthe nodular shaped particles ranging in diameter from .25v to .30 micronhad deteriorated 41%; whereas the original tensile strength of thematerial containing the larger acicular shaped particles onlydeteriorated 9% to' 16%. The material containing the smaller particlesof zinc oxide developed a yellow cast during-the exposure period;whereas the material containing the larger particlesdid not undergo anycolor change. I

These results are surprising since in the paint and lacquer field thetendency is. to increase-the hidingpower by decreasing the size of thepig- 0' ment particles. Therefore, one skilled in the art who wasconfronted with the problem of producing 'a shade cloth material capableof filtering ultra violet light to prevent tendering would undoubtedlyresort to thesmaller pigment particles to accomplish increased hidingpower.

It is probable that the yellowcolorwhich develops in the. case ofmaterial containing the smaller particles of zinc oxide results from thedecomposition of the nitrocellulose binder rather than any color changeof the pigment.

In order to make a wide range of colors in window shade material it isnecessary to blend 'thezinc oxide pigments with various coloredpigments, such as carbon black, bone black,

chrome green, chrome yellow, ultramarine blue, .iron oxide and variouscolored lakes.

as the total pigment content:

The whitejmaterial containing the smaller zinc xi i ment particles haddefinitely yellowed at the endjofthe- 40 weeks exposure and the simnoti9;ny p tt'antial yellowing during the 1 same per-loch,

Material whi'ch deteriorates more than 315%311' fig i fle kst 'e'ngthpon 40 weeks of- Florida ex- 1 him] tensile Tensile Smngth-"m'er 0 WeeksTensile strength after 40 weeks Qstrcnsth F r d exposum Florida exposureDiameter-oi nodular zlncox ide particles in V f I I coating 7 h 1Percent Percent W F. W. and F. W. F. W. and F. deteriora- W. F. 'W.andF. deteriora- 1.1---1. 61 4e no 52 1 m 39 19 L 58 s 47 l. Mgfifii 7o 49119 67 -41 @103 A 9 56 32 8S 7 crue'if the largeparticle size zinc oxide(greater than ;.4 .micron-'m all dimensions) is present in '70 amounts'less than-20% o f theg'total pigment content of thedry coatingcomposition. j The may vary between 20% Pigment'content. o

o low. r thetotal The. advantages of this invention do Inot ac Thecompositions given in the examples are merely illustrative. Any wellknown softener may be used in the composition such as castor oil, blowncottonseed oil, blown rapeseed oil, or the like, but it is preferred toemploy a so-called solvent softener, such as dibutyl phthaiate, dibutyltartrate, etc., and resinous plasticlzer since the solvent softenerstend to reduce the tendency of the shade cloth to curl as is disclosedin U. S. Patent 2,033,170.

To obtain the improved results of the present invention, it has beenfound that zinc oxide, either the pure or leaded varieties, must beemployed. The zinc oxide pigment may be either of acicular or nodularshape. In the case of acicular shaped particles of zinc oxide, thesmallest dimension (width) of the particle should not be less than .4micron.

-'The proportions given in the example are merely illustrative and maybe varied over a wide range as will be readily apparent to those skilledin the art, the proportions being governed by the desired degree oftranslucency. In .the case of equal weights of coating on thewinproduced in accordance with the present invention is the resistanceof the material to tendering upon prolonged exposure to sunlight andheat, and a much greater life than window shade material produced inaccordance with the prior art. A further advantage is resistance toyellowing upon prolonged exposure to sunlight.

The present invention has been described with respect to shade cloth,but it will be apparent that the invention applies to other types ofcellulose derivative coated fabrics and the term "window shade material"as used herein and in the appended claims is intended to includecellulose ester coated fabrics in general having properties'simiiar toshade cloth, such as, e..g., sign cloth used in buses, trolley cars,etc.,as illuminated signs.

It is apparent that many widely different emposed thereon consistingessentially of cellulose nitrate, a plasticizer, and pigment, at least20% of the said pigment comprising zinc oxidehaving a particle sizegreater than .4 micron and less than about 3.2 microns in any onedirection.

2. A window shade materialresistant to tendering and color changecomprising a fabric parts, at least 20% of total pigment contentconsisting of zinc oxide having a particle size greater than .4 micronand less than about 3.2 microns in any one direction.

ROBERT L. LESTER.

